Introduction to Python Functions

Because copy-pasting code is so last semester

Danilo Freire

danilo.freire@emory.edu

Emory University

February 07, 2025

Welcome to Python Functions!
Let’s Code Smarter 🧠

Today’s Journey

Why Functions? ♻️
[Function Anatomy] 🔍
[Parameters vs Arguments] ↔︎️
[Live Coding] 🎮
[Best Practices] ✅
[Q&A + Exercises] 🏋️

Why Functions?

The Repetition Nightmare 😱

# Bad Code Alert! 🚨
print("Welcome Alice!")
print("Welcome Bob!")
print("Welcome Charlie!")
# ... repeats 997 more times ...

Problems: - 🤦 Error-prone updates - 📏 1000 lines of same code - 😵 Hard to maintain

Functions to the Rescue! 🦸

# Clean Solution ✨
def welcome(name):
    print(f"Welcome {name}!")

welcome("Alice")
welcome("Bob")
welcome("Charlie")

Benefits: - ♻️ Reusable code - 📦 Organized logic - 🔄 One change updates all - 📖 Readable structure

Function Anatomy 🔍

Building Blocks of a Function

def calculate_bmi(weight, height):
    """Calculate Body Mass Index"""
    bmi = weight / (height ** 2)
    return bmi

Parameters vs Arguments ↔︎️

Parameters
(Recipe Ingredients)

def greet(name, greeting="Hello"):
    # name and greeting are parameters
    print(f"{greeting}, {name}!")

Arguments
(Actual Ingredients)

greet("Alice", "Hi")  # Positional
greet(greeting="Bonjour", name="Bob")  # Keyword

Let’s Code Together! 🎮

Exercise 1: Area Calculator

def calculate_area(length, width):
    # Your code here...
    return ???

# Test cases
print(calculate_area(5, 4))  # Should return 20
print(calculate_area(3, 7))  # Should return 21

# Solution
def calculate_area(length, width):
    return length * width

Exercise 2: Smart Greeter 🤓

def create_greeting(name, age, city="Unknown"):
    # Return message like:
    # "Hello Alice (25) from Paris!"
    ???

print(create_greeting("Alice", 25, "Paris"))  
# "Hello Alice (25) from Paris!"
print(create_greeting("Bob", 30))  
# "Hello Bob (30) from Unknown!"

# Solution
def create_greeting(name, age, city="Unknown"):
    return f"Hello {name} ({age}) from {city}!"

Pro Tips & Pitfalls ⚠️

Best Practices ✅

Single Responsibility
One function = One task
Meaningful Names
calculate_tax() not do_stuff()

Docstrings 📄

def convert_currency(amount, rate):
    """Convert amount using exchange rate

    Args:
        amount (float): Money to convert
        rate (float): Exchange rate

    Returns:
        float: Converted amount
    """
    return amount * rate

Common Pitfalls 🕳️

Mutable Defaults

# Dangerous 🚨
def add_item(item, lst=[]):
    lst.append(item)
    return lst

# Safe ✅
def add_item(item, lst=None):
    lst = lst or []
    lst.append(item)
    return lst

Return vs Print

# Bad - Can't reuse value 🚫
def double(x):
    print(x * 2)

# Good - Returns value ✅
def double(x):
    return x * 2

Quick Quiz! ❓

What does this print?

def mystery(x=[]):
    x.append(1)
    return x

print(mystery(), mystery())

Answer:
[1, 1] [1, 1]
Because default list is created once!

Next Steps 🚀

Keep Learning!

📚 Real Python Functions Guide
🎥 Corey Schafer Functions Tutorial
💻 Practice on Codewars
(Search for “Python functions”)

Thank You! 😊

Questions?
Let’s Code!
Exercise Solutions

Appendix: Solutions

Area Calculator

def calculate_area(length, width):
    return length * width

Smart Greeter

def create_greeting(name, age, city="Unknown"):
    return f"Hello {name} ({age}) from {city}!"

Back to Start ```